@Florent for the 64 bit versions of uefi, you would replace ipxe.efi with snp.efi or snponly.efi in the config file and then restart the dns server.
The difference between snp.efi and snponly.efi is that the snponly.efi will only init the network interface where the snponly.efi was downloaded from, where the snp.efi will init (and try to boot from) all interfaces in the target computer.